How Do Paternity Tests Work at Crime Labs?

Do you need a character’s paternity to come into question to thicken the plot for your crime fiction book? This post tells you about the different types of paternity testing, how paternity testing works, where to send your samples for forensic paternity testing, and if secret DNA samples are okay to use.

Your amateur sleuth thinks that someone involved in the case is their long-lost father.

There’s a pregnant murder victim and your detective thinks that the killer is the father of the baby.

You want to make sure the paternity testing in your book is accurate but you’re not sure how it works.

Is paternity testing different than regular DNA testing? How long do paternity results take? What kind of DNA samples do the labs use for testing?

In this post, I discuss the differences between forensic and nonforensic paternity, what types of labs perform paternity testing, how paternity testing works, and how long paternity results take.

The Different Types of Paternity Testing

A paternity test uses genetic information (DNA) to determine if a parental relationship exists, either mother-child or father-child.

Paternity testing does not test for other types of familial relationships, such as grandparents, cousins, full or half siblings, etc. That’s called kinship testing and is a different type of DNA analysis.

There are two different situations in paternity testing: nonforensic paternity and forensic paternity.

In nonforensic paternity testing, samples from the child and parent(s) are submitted to a private lab in a situation where the parentage of a child is in question. The results are often used in custody and child support cases.

The main sample type submitted for nonforensic paternity testing is a cheek swab (usually two to four total) because it’s the least invasive method. The image for this blog posts a person getting a cheek (buccal) swab collected if you need to describe it for your books.

Forensic paternity testing is used in criminal casework. Examples of cases that might be submitted to a crime lab are sexual assaults resulting in pregnancy, incest, and homicides with a pregnant victim.

Sample types that might be submitted to the crime lab include cheek swabs, blood samples, or tissue samples. The results of forensic paternity testing are used to charge someone with a crime.

What Types of Labs Perform Forensic Paternity Testing?

Crime labs can perform forensic paternity testing for casework, but not all crime labs have this technology online.

Paternity testing is different than regular forensic DNA testing and has different lab protocols and additional accreditation standards and training requirements.

Law enforcement should call and ask their local crime lab if they provide this type of testing prior to submission.

My old state crime lab was on the small side, and we didn’t offer paternity analysis as a service. We didn’t get enough cases to justify having it online.

Private DNA labs perform nonforensic DNA testing for a fee. Most hospitals do not perform paternity testing.

Law enforcement agencies have the option to send their forensic paternity cases to private labs, either because their local crime lab doesn’t provide forensic paternity testing or they want the results back sooner.

How is Paternity Testing Different than Regular Casework in a Crime Lab?

In a nonpaternity case submitted to the crime lab, the end goal is to find out who left DNA at the crime scene. Crime scene samples (unknowns) are compared to reference samples (knowns) to see if there is a match.

Crime scene evidence is first examined for the presence of body fluids and other biological materials. This type of analysis is called serology. If any of the serology tests are positive, the samples are taken on for DNA testing.

In paternity casework, the sample types are ALL reference samples. We know who the samples came from. No serology testing is performed.

The end goal is to determine if a parental relationship exists between known individuals.

How Long Does a Paternity Test Take?

For forensic paternity casework that is submitted to a crime lab, the turnaround time will vary and depends on a lot of factors.

Without a backlog, I’d say anywhere from 3-5 full business days for paternity testing. In your fiction book you could have them rush it and speed it up to 2 business days.

In nonforensic paternity, which is performed by private labs who charge a fee, the turnaround time can be faster. Results can be back in as little as 1 business day. Some labs even offer same day results for a hefty rush fee.

Are Secret DNA Samples Okay to Use?

I get asked a lot if “secret” DNA samples are okay to use. I define secret DNA samples as samples that are collected without the person knowing about it, such as a discarded drinking container or other personal item.

In general, the answer is yes.

However, if the DNA samples are part of a criminal investigation, an amateur detective can’t collect/submit them for chain of custody reasons. It needs to be law enforcement.

If it’s nonforensic paternity and a character in your book just wants to know if there’s a parental relationship, then the amateur detective can collect and submit the samples to a private lab (not the crime lab). If there is a legal reason for needing to know the parental relationship (maybe for inheritance reasons), then the samples must be submitted in a more formal manner.

Summary

You should now know the differences between forensic and nonforensic paternity, what types of labs perform paternity testing, how paternity testing works, how long the results take, and how to use secret DNA samples.

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